Replicated Data Should Be Read-only

It is preferable that data architecture includes an authoritative source for data. This is where all updates should be directed. Allowing users to update replicated data unnecessarily complicates the replication environment and introduces potential data integrity problems. In a distributed environment, using a single source to guarantee data consistency is easier than managing updates in a multiple data source environment.

For example, if you have a replicated database that can be updated from multiple locations, you must consider the expected behavior when two people update the same record at the same time. Possible outcomes could include the following:

• Allowing the first update to succeed and undoing the last update (FIFO)

• Allowing the last update to overwrite the first update (LIFO)

• Canceling both updates

• Moving both updates to another table and allowing an administrator to determine the outcome

Obviously, multiple deviations on the above outcomes are possible. What is important to note is that they will make your data architecture a lot more complicated than it needs to be. By utilizing an authoritative source, other data sources can synchronize to the source of record, ensuring consistency.